The invention disclosed herein pertains to a tilting pad journal bearing of the type comprising of a bearing shell in the form of a supporting ring member and a plurality of circumferentially spaced shaft supporting pads arranged within the ring member. Instead of the bearing interfaces between the pads and the shaft being lubricated by immersing the entire interior bearing assembly as is generally done in tilting pad bearings, the new bearing design disclosed herein provides for injecting lubrication directly onto the shaft between the trailing and leading ends of the circumferentially spaced apart tilting bearing pads.
The type of bearing to which the invention applies is one wherein the pads tilt through a small angle so as to create a thin wedge shape opening which is thickest between the leading end of the pads and the shaft and which tapers to a thinner wedge at the trailing end of the pad. This well known phenomena is involved with developing a film of oil between the bearing surface of the pad and the shaft such that the load is actually supported on the oil film. Of course, because the film of oil is sheared as the oil is dragged through the bearing interface, the oil temperature rises. As is well known, if the oil temperature rises sufficiently, its viscosity falls, and if the temperature rise is high enough, the oil thins to a point where there is a direct rubbing of the metal shaft on the metal bearing surfaces, resulting in greater friction which may increase the bearing temperature to destructive level.
In conventional tilting pad bearings wherein the pads are lubricated by flooding them and all other parts of the bearing assembly with oil, the oil is subjected to shearing and to a concomitant increase in its temperature simply by running over parts which are not even involved in creating low friction conditions at the interface of the shaft and the bearing pads. It is not unusual for a tilting bearing supporting a long shaft, such as one that is used to connect a turbine to an alternator of megawatt capacity, to experience power consumption on the order 0.3 to 0.5 percent of the total power output of the turbine.
It is known that some power loss in tilting pad bearings results from churning of the oil after it passes out from underneath the trailing end of the pads. Churning imparts energy to the oil and elevates its temperature. Another problem in connection with lubricating a tilting pad bearing is known as the hot oil over carry over problem. Since it is necessary to have some space between the leading and trailing edges of the circumferentially spaced apart bearing pads hot oil emerging from the pad and shaft interface at the trailing end of one pad has a tendency to be carried by the shaft under the leading end of the next ensuing pad. It would be most desirable if all of the oil introduced at the leading ends of the pads were freshly cooled oil instead of oil which has emerged from a preceding pad where it has gained a substantial amount of heat.